The present invention relates to a machine for piercing a taphole for a shaft furnace, and more particularly to the so-called lost rod method used for piercing a taphole for a shaft furnace used in the production of steel. The lost rod method comprises blocking the taphole with taphole clay. Before the taphole clay has fully hardened, a metal rod is driven into and through this clay to a desired distance into the shaft furnace. At the appropriate time, the metal rod is extracted to open the taphole. The machine of the present invention comprises a mounting which has a support for the piercing rod at the front end. A rear support which can move slidably on the mounting is provided with coupling means for the rear end of the piercing rod. A clamp is provided which is slidable on the mounting and is designed to grip the piercing rod at any place between the front support and the rear support.
The prior art machines used previously to the present invention for this lost rod method are substantially conventional drilling apparatuses (i.e., drilling apparatuses designed for working with a drill bit). These conventional drilling machines have undergone appropriate adaptations and modifications to make them suitable for use in the lost rod method.
The main working members of these drilling machines is comprised of a chuck, a coupling clamp for the piercing rod, and a bi-directional pneumatic hammer. It should be noted that a high powered pneumatic hammer is required to deliver the large forces necessary for the insertion and extraction of the lost piercing rod.
In most cases, the above machines do preserve the possibility of being able to use a drilling apparatus with a bit. This feature is desirable in the cases where a taphole must be reformed or the taphole's location must be changed. Also, it is desirable to be able to work with a conventional bit if for some reason or another, the lost rod method cannot be used.
However, a powerful, large pneumatic hammer, as is used on these prior art machines, is not without considerable drawbacks. One major drawback is that the pneumatic hammer exerts considerable amount of stresses and vibrations on the equipment. As a result, in particular, the rod-coupling clamp is subjected to rapid wear. Another major drawback is that the pneumatic hammer is extremely noisy, and very often cannot conform to ever-stricter standard aimed at reducing the noise level in an industrial environment.
The patent application EP-0-379-018 and Luxembourg patent application 87 927 corresponding to U.S. application Ser. No. 462,415 filed Jan. 9, 1990, all the contents of which are incorporated herein by reference, provides an excellent method for extracting the piercing rod from a shaft furnace. This method relies on the action of a silent hydraulic jack to extract the piercing rod in several phases by means of a to-and-fro motion of a clamp acted upon by this silent hydraulic jack. This eliminates the need of a bi-directional pneumatic hammer since the pneumatic hammer is no longer required for use in the extraction of the piercing rod. The pneumatic hammer is still, however, required for efficient and rapid installation of the piercing rod.
The disadvantages of the pneumatic hammer, previously discussed, make it desirable to eliminate the percussion of the pneumatic hammer during the insertion phase of the piercing rod into the taphole. It is possible to subject the working member to a much more powerful driving means to advance the working member coupled to the piercing rod along the mounting in the direction of the taphole without vibrations into the semi-hardened sealing clay. Unfortunately, because of the length of the piercing rod, a too strong driving force can cause the piercing rod to buckle and could then be permanently blocked in a position which would not allow the piercing rod to be further driven into or extracted from the rapidly hardening taphole clay.
A better solution to the foregoing problem as discussed above, is suggested in the Luxembourg patent application LU-87-915, filed on Apr. 3, 1991, corresponding to U.S. application Ser. No. 862,487 filed Apr. 2, 1992, all the contents of which are incorporated herein by reference. This patent application comprises a bi-directional clamp whose reciprocating to-and-fro motion, produced by a hydraulic jack at the front of the mounting, is used both for the insertion and for the extraction of the piercing rod. U.S. application Ser. No. 862,487 does make it possible to eliminate the noisy and clamp-damaging pneumatic hammer. A disadvantage of the machine described in U.S. application Ser. No. 862,487 is that the bi-directional clamp and the means which actuate the bi-directional clamp always operate in the front region of the mounting. However, this region is a zone which is at risk of being splashed when the molten jet stream escapes from the taphole after extraction of the rod.
The problem of damage due to splashing in the preceding paragraph is resolved in Luxembourg patent application LU-88-029, filed Oct. 31, 1992, corresponding to U.S. application Ser. No. 968,984 filed Oct. 30, 1992, all the contents of which are incorporated herein by reference. This machine basically comprises two jacks. The first jack is mounted in a sliding manner on the mounting in such a way that the first jack can move along the mounting when urged by the second jack. The piercing rod is no longer extracted by a reciprocating to-and-fro motion of the clamp, but by a continuous withdrawal motion of the clamp under the combined action of the two hydraulic jacks. The clamp is cleared from the splash zone at the front of the mounting before the molten jet stream escapes from the taphole. A further advantage is that the extraction of the piercing rod is much speedier, since the extraction is carried out by a continuous movement compared to the intermittent movements involved in the to-and-fro movement by the clamp previously used.
U.S. application Ser. No. 968,984 described above only is involved in the extraction of the piercing rod. The piercing rod is inserted in the same manner as depicted in U.S. application Ser. No. 862,487. The clamp used in inserting the piercing rod under U.S. application Ser. No. 862,487 is acted upon with a reciprocating to-and-fro motion under the action of the first jack, after the first jack has been advanced into the operative position by the second jack.
The method for extraction of the piercing rod provided in U.S. application Ser. No. 968,984 provides satisfactory operation. A drawback of U.S. application Ser. No. 968,984 is that there is a considerable increase in the bulk and overall length of the machine. This is not desirable and can interfere with operation because of the lack of available space around the shaft furnace.